Microplastics promote the invasiveness of invasive alien species under fluctuating water regime

Microplastic pollution and alien plant invasions are two important threats
to terrestrial ecosystems. Microplastics (MPs) alter the physical and
chemical characteristics of soil,  potentially affecting the
performance of alien plants. However, previous studies have overlooked the
impact of weather on invasive plants in areas polluted by MPs. With the
global increase in extreme rainfall events, it is imperative to redefine
the correlation between MPs and invasive plants. Here, we conducted an
experiment in a climate chamber to examine the effects of MPs on the
growth and development of both native and invasive alien plants under a
constant and fluctuating water regime (FWR). The FWR simulated extreme
water pulses during the 2016-2020 growing seasons in Wuhan, China. Our
results indicated that biomass accumulation and roots development were
influenced by water conditions and MPs pollution in both invasive and
native species. The extent of the effects varied between the two groups of
plant species. FWR promoted plant growth and fine root development in
invasive plants but reduced the maximum quantum efficiency of photosystem
II (Fv/Fm) and nonphotochemical quenching (NPQ) indices of native plants.
Moreover, FWR attenuated the negative effects of polybutylene succinate
(PBS, degradable MPs) on biomass and root characteristics (length, surface
area, and tips). FWR compensates for the negative impacts of MPs on the
total and belowground biomass of the invasive species Paspalum
dilatatum and Sphagneticola trilobata, but not on the native
species. Consequently, invasive species showed better performance than
native species in the fine-root development of biomass growth and
chlorophyll fluorescence under the combined effects of MPs and FWR.
Synthesis and Applications. Our findings suggest that MPs pollution
enhances the competitiveness of invasive alien species over the native
species when exposed to pronounced dry-wet water cycle conditions,
potentially affecting the composition and biodiversity of the ecosystems.
Thus, controlling MPs pollution should be a part of the management
strategy to conserve biodiversity and ecosystems.